1. Field of the Invention
The present invention relates to a nitride-based semiconductor light emitting diode (LED) which has high resistance to electrostatic discharge (ESD).
2. Description of the Related Art
Because group III-V nitride semiconductors such as GaN have excellent physical and chemical properties, they are considered as essential materials of light emitting devices, for example, light emitting diodes (LEDs) or laser diode (LDs). The LEDs or LDs formed of the group III-V nitride semiconductors are widely used in the light emitting devices for obtaining blue or green light. The light emitting devices are applied to light sources of various products, such as electronic display boards and lighting devices.
However, the LEDs using nitride semiconductors have such a defect that they have much lower resistance to ESD than other compound semiconductors such as GaP and GaAlAs. For example, when a constant voltage of about several hundred volts (more than 100 V) is applied in a forward direction, the nitride semiconductor LED can be destroyed. Further, when a constant voltage of about dozen volts (more than 30 V) is applied in a backward direction, the nitride semiconductor LED can be destroyed. Such a constant voltage can be generated by static electricity which easily occurs in a person's body or a product when a nitride semiconductor light emitting devices such as an LED or LD is handled or used.
Accordingly, in order to suppress the damage of nitride semiconductor LEDs caused by ESD, various researches are being carried out. For example, a voltage regulator diode, in which an electric current can flow in a backward direction, is provided in order to make up for the weakness of nitride semiconductor LEDs with respect to ESD. As for the voltage regulator diode, a Zener Diode is provided, which is connected in parallel to an LED so as to effectively deal with static electricity.
Now, a conventional nitride-based semiconductor LED will be described in detail with reference to FIGS. 1 and 2.
FIG. 1 is a front view of a conventional nitride-based semiconductor LED, and FIG. 2 is a sectional view of the nitride-based semiconductor LED shown in FIG. 1.
As show in FIGS. 1 and 2, the nitride-based semiconductor LED includes an LED 30 and an ESD protecting element 40 which are mounted in parallel on the same surface of a lead frame 50 composed of a pair of anode lead 51 and cathode lead 52. The LED 30 and the ESD protecting element 40 are connected through a wire 60 formed of gold (Au), thereby forming a parallel structure. The ESD protecting element 40 is composed of a Zener diode.
In FIGS. 1 and 2, reference numeral 10 represents a package formed of transparent or opaque synthetic resin, and reference numeral 20 represents a molding material for protecting the LED.
The Zener diode serving as the ESD protecting element 40 is a so-called voltage regulator diode. The Zener diode is one of semiconductor p-n junction diodes and is manufactured so as to exhibit operational characteristics in a breakdown region of p-n junction. Further, the Zener diode obtains a constant voltage by using a Zener effect and operates in p-n junction of silicon at a current of 10 mA. Further, the Zener diode can obtain a constant voltage of 3 to 12 V, depending on a type thereof.
In the conventional nitride-based semiconductor LED, such a Zener diode is connected in parallel to the LED through a wire or the like. Therefore, although a backward current is applied due to static electricity, the Zener diode can prevent the LED from being damaged.
However, when the Zener diode and the LED is mounted in parallel on the lead frame, light emitted from the LED can be absorbed or diffused by the Zener diode, thereby reducing the luminance of the LED.
To solve such a problem, a technique in which an LED and a Schottky diode are formed on the same substrate has been proposed, as shown in FIG. 3B of U.S. Pat. No. 6,593,597. FIG. 3 is a sectional view illustrating the structure of a conventional nitride semiconductor LED shown in FIG. 3B of U.S. Pat. No. 6,593,597.
In the conventional nitride semiconductor LED shown in FIG. 3, an LED and a Schottky diode are formed on the same substrate so as to be connected in parallel to each other. Accordingly, light emitted from the LED is not lost, and the LED can be protected from ESD, thereby enhancing the luminance of the LED.
In such a technique, however, there is a problem that the manufacturing process thereof is complicated. That is, the LED region and the Schottky diode region should be separated from each other. Further, electrode materials forming Schottky contact and electrode materials forming ohmic contact should be separately deposited on a conductive buffer layer, in order to form Schottky junction.